Stable Antiaromatic [24]Hexaphyrin(1.1.0.0.1.0) and Its Metal Complexes.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Coordination Chemistry

Background:

• Hexaphyrins are macrocyclic compounds with unique electronic and structural properties.
• Controlling the aromaticity and stability of hexaphyrin systems is crucial for their application.
• Substituted hexaphyrins offer tunable characteristics for complexation and material science.

Purpose of the Study:

• To synthesize a stable, substituted [24]hexaphyrin with antiaromatic character.
• To investigate the reduction of the [24]hexaphyrin to its aromatic [26] counterpart.
• To explore the coordination chemistry of the synthesized [24]hexaphyrin with metal ions, specifically palladium and rhodium.

Main Methods:

• Base-catalyzed twofold S_NAr reaction for the synthesis of the [24]hexaphyrin.
• Chemical reduction to obtain the [26]hexaphyrin.
• Complexation reactions with palladium(II) and rhodium(I) salts.

Main Results:

• A stable 5,10,23-trimesityl-substituted [24]hexaphyrin was successfully synthesized.
• The [24]hexaphyrin was reduced to an unstable aromatic [26]hexaphyrin, which readily oxidized back.
• The [24]hexaphyrin formed unique bis-Pd^II and tris-Rh^I complexes.
• The bis-Pd^II complex exhibited a strong paratropic ring current.
• The tris-Rh^I complex displayed unusual coordination involving a shared carbonyl group.

Conclusions:

• Stable antiaromatic hexaphyrins can be synthesized and serve as versatile ligands.
• The interconversion between antiaromatic and aromatic hexaphyrins highlights their dynamic electronic nature.
• The unique coordination geometries in the metal complexes offer insights into novel supramolecular architectures.